Delay line

ABSTRACT

An improved ultrasonic delay line comprising a solid glass body having one or more slits in the side walls extending inwardly from the outer edge faces of the body. The slits are arranged in the path of the propagating ultrasonic energy so as to effectively increase the number of energy transmission paths in the body by acting as additional energy reflecting surfaces. The slits extend the effective length of the delay line. The slits also operate to reduce undesired cross-coupling between the input and output transducers.

United States Patent Gibson 1 June 20, 1972 [54] DELAY LINE [72] Inventor: Rodney William Gibson, Haywards Heath,

England [73] Assignee: U.S. Philips Corporation [22] Filed: Feb. 12, 1969 [21] Appl.No.: 798,665

[30] Foreign Application Priority Data Feb. 16, 1968 Great Britain ..7,759/68 [52] US. Cl ..333/30 [51] Int. Cl. ..i-l03h 9/30 5 8] Field of Search ..333/30, 72

[56] References Cited UNITED STATES PATENTS 3,522,557 8/1970 Duncan ..333/3O 3,025,479 3/1962 Wolfskill ..333/3O 2,907,958 10/1959 Skaggs ..333/30 2,927,284 3/1960 Won-ell et al ..333/30 2,826,744 3/ 1958 Arenberg .333/30 2,839,731 6/1958 McSkimin.. ..333/30 2,965,851 12/1960 May ..333/30 Primary Examiner-Herman Kari Saalbach Assistant Examiner-C. Baraff AttorneyF rank R. Trifari [57] ABSTRACT An improved ultrasonic delay line comprising a solid glass body having one or more slits in the side walls extending inwardly from the outer edge faces of the body. The slits are arranged in the path of the propagating ultrasonic energy so as to effectively increase the number of energy transmission paths in the body by actingas additional energy reflecting surfaces. The slits extend the effective length of the delay line. The slits also operate to reduce undesired cross-coupling between the input and output transducers.

19 Claims, 5 Drawing Figures PliTENTEllJuuzo I972 INVENTOR.

.RODNEY WILUAM GIBSON DELAY LINE This invention relates to ultrasonic delay lines of the type using a solid medium such as quartz or glass through which an acoustic signal wave is made to travel to provide a time delay between the application of the wave and its extraction. In such delay lines it is known to shape the solid medium so as to provide internal peripheral reflective surfaces for the ultrasonic wave in order to fold the wave over a plurality of legs to increase the length of the transmission path through the medium and thus increase the wave delay with a minimum mass of solid medium.

It is also known to increase the length of the transmission path of an ultrasonic wave .by including specially shaped openings in the solid medium to provide additional reflective surfaces. In this case such openings have to be very accurately positioned and dimensioned to ensure proper operation.

In connection with such delay lines there arises a number of problems. Some of these concern the solid medium itself and its thermal properties. Delay lines using wavelengths equivalent to several Megahertz require very accurate dimensioning to reduce internal energy scatter and give an accurate source of extraction. This requires a solid medium having a very low temperature coeificient. A special glass having such properties is available but it is relatively costly for use in mass production so that any design steps that will allow an overall reduction in the mass of the delay medium will not only in itself reduce thermal problems but will also reduce overall costs.

In certain color television receiver systems a prescribed signal delay is required so that the delay line has to provide stable operation and yet lend itself to mass production at a very low cost.

Another problem which confronts the designer of such delay lines is the prevention of direct signal coupling between the application and extraction points of the signal which can result in the desired delayed signal being masked by a strong undelayed signal arriving at the extraction point. A further problem is'the suppression of alternative signal paths which contribute a train of secondary spurious signals each having a different delay and which make extraction of the wanted delayed signal difficult. v

The purpose of this invention is to provide a simple delay line construction in which the overall mass of the delay line medium is reduced in a manner which will also allow greater freedom from expensive manufacturing processes as well as providing enhanced electro-acoustical performance.

According to this invention there is provided an ultrasonic delay line using a solid medium through which an ultrasonic signal wave is made to travel and which is reflected over a plurality of paths to increase the time delay between the application point of the ultrasonic signal and its point of extraction, wherein the path followed by the ultrasonic waves includes at least one reflecting surface constituted by the side wall or face of a slit extending inwards from an edge face of the solid medi- In order to make maximum utilization of a given delay line mass, the delay line may include several slits arranged so that both side walls of the slits can be used as reflective surfaces. Furthermore, if the geometrical pattern of the reflected signal legs or path is so arranged that an odd number of legs exists between reflections on the same or associated slit wall, this gives the advantage that the angular orientation of the slit is non-critical and it displays self-cancelling properties for minor errors. 1

Furthermore, the use of slits to provide reflective walls also has the advantage of reducing spurious secondary signals in that a greater control can be exercised over the required signal path by the very high damping barrier provided by the absence of any delay line medium forming the slit. This reduces any signal transference across the slit to a value far below the minimum requirements.

It should be noted that the use of notches introduced in the edge surfaces of a solid medium for a delay line to reduce secondary waves from reaching the output transducer is known per se. However, these notches do not constitute reflecting walls for the desired signaL' Examples of this invention will now be described with reference to the accompanying drawings in which FIG. 1 is a plan view of a substantially rectangularly shaped delay line showing a simplified embodiment of applicant's invention.

FIG. 2 is a plan view of a substantially rectangularly shaped delay line showing two slits for further increasing the length of the delay line of FIG. 1.

FIG. 3 is a plan view of a delay line having five reflecting faces for further increasing the length of the delay line of FIG. 1

FIG. 4 is a plan view of a delay line shaped as a. parallelogram having four slits.

FIG. 5 is a plan view of a delay line having five edges and a central slit. L

FIGS. 1 to 5 show five different embodiments of delay lines according to this invention. Each Figure has certain design features which will be discussed below.

FIG. 1 shows a solid body 1 made, for example, of glass and having a substantially rectangular cross-section. Two comers of the body 1 are beveled and transducers A and B are arranged on the surfaces 14 and 15, respectively. The surfaces 14 and 15 are at respective angles of 135 to the surfaces l7, l8 and 18, 19 of the body 1. The input transducer A has an electric signal applied to it which is converted by the transducer into an acoustic ultrasonic signal. This acoustic signal propagates in the form of a wave through the body 1 and after a number of reflections it reaches the transducer B which reconverts it into an electric signal. The time required for the acoustic ultrasonic wave to cover the entire path (shown in dotted lines) from the transducer A to the transducer B determines the delay time between the application of the electric input signal at the transducer A and the electric output signal recovered at the transducer B. Use is preferably made of piezo-electric transducers which are so polarized that shear mode vibrations are produced so that the overall reflection at each of the reflective surfaces occurs without energy conversion of the shearvibrations into longitudinal vibrations.

According to this invention, a slit 2, in the form of a saw-cut having plane parallel walls, is provided at the plane of symmetry in the body 1 so that the waves originating from the transducer A first reflect at the left-hand wall of the slit 2 and then at the rectangular walls l6, l7, l8, l9, and 20 of the body l, whereupon they are reflected from the right-hand wall of the slit 2 and finally strike the transducer B. The energy path from transducer A to transducer B is made up of eight reflected signal legs shown by dashed lines with arrowheads. It will be apparent from FIG. 1 that an increased path length for the ultrasonic wave is thus obtained in a simple manner. Moreover, secondary waves are suppressed by the slit 2. The angle at which the ultrasonic wave strikes the various reflective surfaces is always 45. However, in this embodiment the angle 3 of between the slit 2 and the surfaces 16 and 20 must be very accurately defined in order that the waves may follow the path indicated.

In the delay line of FIG. 2, the signal paths (shown in dotted lines) are obtained by providing two slits 2 and 4 at suitably chosen areas at right-angles to the long surfaces 21 and 22 of the delay line medium 1. In thisembodiment the ultrasonic waves also strike the reflective surfaces at angles of 45. However, afler reflection at one wall of the slit 2, an odd number of signal legs (five) occurs before reflection at the other wall of the slit 2. As a result, the orientation of the angles 5 and 6 of 90 is not critical and the angular errors introduced into the reflected signals are cancelled automatically. In this construction, the slits 2 and 4 also cause a reduction of secondary (spurious) signals, and moreover the formation of any direct or secondary transmission path between the input transducer A and the output transducer B is prevented.

The delay line construction of FIG. 3 provides an increased length of the transmission path while retaining the advantages of the delay line constructions shown in FIGS. 1 and 2. In this case, the body 1 has a square cross-section (a corner of the square being denoted by x-x) and the opposite corner of the square is removed so that an additional wall 31 is formed on the body 1 which is at an angle of 135 to the walls 32 and 33. The transducers A and B are arranged side by side on the wall 31, while a slit 8 is provided at right angles to and approximately centrally of a wall 34 of the body 1 and extends approximately as far as half the length x into the body 1. The ultrasonic waves again follow the path indicated by dotted lines.

Either the transducer A or the transducer B may be used as input or output. Since the number of signal legs between the reflections at one wall and those at the other wall of the slit 8 is odd (five), the orientation of the angle 7 of 90 between the slit 8 and the surface 34 is not critical because the angular error introduced into the signal wave is automatically canceled. This self-canceling effect is illustrated in FIG. 3, in which the slit 8 is purposely slightly tilted. A practical embodiment of a glass delay line of this construction for use in a PAL color television receiver system has the following approximate dimensions:

x=33 mm,y= 15 mm, andz=6 mm.

The width of the slit 8 is approximately 1 mm and this slit extends over approximately 15 mm into the delay line 1. The electric characteristics give a delay of one line period, i.e., approximately 64 sec, at a band center frequency of 4.4 Mc/s.

FIG. 4 shows a body 1 in the form of a rectangular prism having a cross-section in the form of a parallelogram whose sides 41, 42 and 43, 44 respectively are at angles of 45 to each other. Slits 8, l and 9, 11, respectively, are provided at right angles to the side faces 42 and 44. In this delay line, only one side wall of each of the slits 8, 9, 10, and 11 is used at a time. An input transducer A is arranged for injecting an ultrasonic signal which follows the path shown in dotted lines and which is extracted by the output transducer B. In this construction, any angular displacements of the slits are not automatically canceled and the angles are therefore critical, but the remote positioning and interspersion of the slits between the inputtransducer A and the output transducer B provides a high degree of decoupling for spurious (secondary) signals when compared with known delay lines.

The surface of the delay line of FIG. has a cross-section in the form of a pentagon having two parallel sides 51 and 52 and a third side 53 at right angles to the sides 51 and 52, while the fourth and fifth sides 54 and 55 are at angles of 135 to the sides 51 and 52, respectively. The latter sides 54 and 55 support the transducers A and B, respectively. According to the invention, a slit 56 is positioned at the intersection of the sides 54 and 55 and extends into the body 1 parallel to the sides 51 and 52 over a distance approximately equal to half the length of the sides 51 and 52. The path followed by the ultrasonic waves is shown in dotted lines. Small angular displacements of the surfaces 51 and 52 again substantially do not influence the overall delay time and the direction in which the waves strike the output transducer B. Also, the slit 56 prevents the direct coupling of scattered radiation from the input transducer A to the output transducer B.

it will be evident from the foregoing that delay lines constructed in accordance with this invention can be easily and economically mass produced. A comparatively long rod of delay line medium may be profiled, for example, in the desired shape, while the slits may be accurately arranged throughout its length. The method of manufacturing separate delay lines then merely resides in parting off portions of the rod to the desired thickness. This results in a high reproducibility of components of individual delay lines.

The invention is not limited to the delay line described consisting of a single layer, but the advantages of this invention may also be obtained in delay lines consisting of several layers, the path followed by the signal in one layer then being reflected at a suitable point to a further layer so that it can pass on through this further layer before it is extracted.

What is claimed is:

1. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body and positioned so as to provide substantially complete reflection of the desired energy from opposite faces thereof to the edge walls thereby to redirect said energy through the body to increase the delay between said first and second points.

2. A delay line as claimed in claim 1 wherein the wall slit is arranged relative to one or more reflecting edge walls of the body so as to produce an odd number of said paths between a reflection from one face of the slit and a subsequent reflection from the same or opposite face of said slit.

3. A delay line as claimed in claim 2 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.

4. A delay line as claimed in claim 1 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.

5. A delay line as claimed in claim 1 wherein the wall slit is located in the plane of symmetry of the body,said delay line further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.

6. A delay line as claimed in claim 1 wherein said body includes a second wall slit extending inwards from an outer edge wall and positioned so that the ultrasonic energy is reflected off of opposite faces of the second slit.

7. A delay line as claimed in claim 1 wherein the wall slit is arranged in the body relative to one or more reflecting edge walls thereof so as to multiply reflect the desired energy from said wall slit to produce an odd number of said paths between a first reflection from one face of the slit and a second subsequent reflection from a face of the slit.

8. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body to reflect the desired energy to the edge walls thereby to redirect said energy through the body, said wall slit being arranged in the body so as to intercept ultrasonic energy propagating along given undesired transmission paths between said first and second energy points of the body thereby to reduce any direct coupling of scattered secondary ultrasonic energy between said first and second points.

9. An ultrasonic delay line comprising a solid body having at least five energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, two of said edge walls being parallel to each other and orthogonal to a third edge wall, the fourth and fifth edge walls each being at an angle of approximately to a respective one of said parallel edge walls, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit extending centrally inwards into the body orthogonal to said third edge wall and arranged to block the passage therethrough of impinging ultrasonic energy thereby to redirect said energy through the body.

10. A delay line as claimed in claim 9 wherein said wall slit extends inwardly from said third outer edge wall.

11. A delay line as claimed in claim 9 wherein said fourth and fifth edge walls intersect one another and said wall slit extends inwardly from the intersection of said fourth and fifth edge walls.

12. A delay line is claimed in claim 1 wherein said body has a generally rectangular shape and a second wall slit extending inwards from an outer edge wall of the body so as to reflect the ultrasonic energy, the first and second wall slits extending inwards from opposite parallel edge walls of the body.

13. A delay line as claimed in claim 9 further comprising first and second electromechanical transducers coupled to said body at one or more edge walls other than the edge wall from which the wall slit extends.

14. A delay line as claimed in claim 11 further comprising first and second electromechanical transducers coupled to said body at said fourth and fifth edge walls, respectively, thereby to reduce direct coupling of scattered secondary ultrasonic energy between the transducers.

15. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body thereby to redirect said energy through the body, and a second wall slit extending inwards from an outer edge wall of the body so as to reflect the ultrasonic energy, the first and second wall slits extending inwards from opposite parallel edge walls of the body, and wherein said body has a parallelogram cross-section and said first and second wall slits extend orthogonally inwards from the longer pair of parallel edge walls.

16. A delay line as claimed in claim 12 further comprising first and second electromechanical transducers coupled to said body at said first and second points which are located on edge walls other than the edge walls from which the wall slits extend.

17. An ultrasonic delay line comprising a solid body having at least five energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, two of said edge walls being parallel to each other and two other edge walls being at right angles thereto, a fifth edge wall being at an angle of approximately to each of two adjacent edge walls, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of mu]- tiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit extending into the body centrally of and orthogonal to one of the edge walls located opposite to the fifth edge wall and arranged to block the passage therethrough of impinging ultrasonic energy thereby to redirect said energy through the body.

18. A delay line as claimed in claim 17 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively,

19. A delay line as claimed in claim 18 wherein said first and second energy points are located on the fifth edge wall. 

1. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body and positioned so as to provide substantially complete reflection of the desired energy from opposite faces thereof to the edge walls thereby to redirect said energy through the body to increase the delay between said first and second points.
 2. A delay line as claimed in claim 1 wherein the wall slit is arranged relative to one or more reflecting edge walls of the body so as to produce an odd number of said paths between a reflection from one face of the slit and a subsequent reflection from the same or opposite face of said slit.
 3. A delay line as claimed in claim 2 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.
 4. A delay line as claimed in claim 1 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.
 5. A delay line as claimed in claim 1 wherein the wall slit is located in the plane of symmetry of the body, said delay line further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.
 6. A delay line as claimed in claim 1 wherein said body includes a second wall slit extending inwards from an outEr edge wall and positioned so that the ultrasonic energy is reflected off of opposite faces of the second slit.
 7. A delay line as claimed in claim 1 wherein the wall slit is arranged in the body relative to one or more reflecting edge walls thereof so as to multiply reflect the desired energy from said wall slit to produce an odd number of said paths between a first reflection from one face of the slit and a second subsequent reflection from a face of the slit.
 8. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body to reflect the desired energy to the edge walls thereby to redirect said energy through the body, said wall slit being arranged in the body so as to intercept ultrasonic energy propagating along given undesired transmission paths between said first and second energy points of the body thereby to reduce any direct coupling of scattered secondary ultrasonic energy between said first and second points.
 9. An ultrasonic delay line comprising a solid body having at least five energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, two of said edge walls being parallel to each other and orthogonal to a third edge wall, the fourth and fifth edge walls each being at an angle of approximately 135* to a respective one of said parallel edge walls, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit extending centrally inwards into the body orthogonal to said third edge wall and arranged to block the passage therethrough of impinging ultrasonic energy thereby to redirect said energy through the body.
 10. A delay line as claimed in claim 9 wherein said wall slit extends inwardly from said third outer edge wall.
 11. A delay line as claimed in claim 9 wherein said fourth and fifth edge walls intersect one another and said wall slit extends inwardly from the intersection of said fourth and fifth edge walls.
 12. A delay line is claimed in claim 1 wherein said body has a generally rectangular shape and a second wall slit extending inwards from an outer edge wall of the body so as to reflect the ultrasonic energy, the first and second wall slits extending inwards from opposite parallel edge walls of the body.
 13. A delay line as claimed in claim 9 further comprising first and second electromechanical transducers coupled to said body at one or more edge walls other than the edge wall from which the wall slit extends.
 14. A delay line as claimed in claim 11 further comprising first and second electromechanical transducers coupled to said body at said fourth and fifth edge walls, respectively, thereby to reduce direct coupling of scattered secondary ultrasonic energy between the transducers.
 15. An ultrasonic delay line comprising a solid body having a plurality of energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected inTernal transmission paths for delaying said ultrasonic energy, an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit arranged to block the passage therethrough of impinging ultrasonic energy and extending inwards from an outer edge wall of the solid body thereby to redirect said energy through the body, and a second wall slit extending inwards from an outer edge wall of the body so as to reflect the ultrasonic energy, the first and second wall slits extending inwards from opposite parallel edge walls of the body, and wherein said body has a parallelogram cross-section and said first and second wall slits extend orthogonally inwards from the longer pair of parallel edge walls.
 16. A delay line as claimed in claim 12 further comprising first and second electromechanical transducers coupled to said body at said first and second points which are located on edge walls other than the edge walls from which the wall slits extend.
 17. An ultrasonic delay line comprising a solid body having at least five energy reflecting edge walls and composed of ultrasonic wave energy transmitting material, two of said edge walls being parallel to each other and two other edge walls being at right angles thereto, a fifth edge wall being at an angle of approximately 135* to each of two adjacent edge walls, said edge walls being arranged to provide a first point for introducing ultrasonic energy and a second point for extracting said energy from the body and further providing a plurality of multiply reflected internal transmission paths for delaying said ultrasonic energy, and an energy reflecting surface positioned in the desired energy transmission path and formed by a wall slit extending into the body centrally of and orthogonal to one of the edge walls located opposite to the fifth edge wall and arranged to block the passage therethrough of impinging ultrasonic energy thereby to redirect said energy through the body.
 18. A delay line as claimed in claim 17 further comprising first and second electromechanical transducers coupled to said body at said first and second points, respectively.
 19. A delay line as claimed in claim 18 wherein said first and second energy points are located on the fifth edge wall. 